1. Field of the Invention
The present invention relates to an isolator and a circulator used in microwave band and millimeter wave band and in particular, to a surface mounting type isolator and a surface mounting type circulator. The present invention also relates to an MIC (Microwave Integrated Circuit) and an MCM (Multi-chip Module) in which a surface mounting type isolator or a surface mounting type circulator is included.
2. Description of the Prior Art
As a conventional microwave band isolator, an MIC isolator using MIC technology is well known.
For example, a prior art reference of such an MIC isolator is disclosed in Japanese Utility Model Laid-Open Publication No. 60-25207.
FIGS. 5A, 5B, and 5C are a plan view, a side view, and a bottom view of the MIC isolator of the prior art reference, respectively.
In FIGS. 5A, 5B, and 5C, reference numeral 51 is a permanent magnet. Reference numeral 52 is a ferrimagnetic substrate having a conductor pattern on one surface thereof. Reference numeral 53 is a non-magnetic grounding conductor plate that securely supports the other surface of ferrimagnetic substrate 52 and functions as a grounding conductor. Reference numeral 54 is a 50-ohm chip resistor. Reference numeral 55 is a junction area portion that is connected to branch lines 56. One terminal of 50-ohm chip resistor is connected to one of branch lines and the other terminal is connected to non-magnetic grounding conductor plate 53 by a conductor not shown in FIG. 5A, 5B, or 5C.
As another prior art reference, an isolator which uses an alumina-ceramic substrate in place of ferrimagnetic substrate and comprises a ferrite column inserted into the hole of the alumina-ceramic is disclosed in JPA-61-288486.
In a MIC, in order to keep the characteristics of semiconductor chips for use, the semiconductor chips are enclosed in an airtight package, whereby a radio frequency circuit using them is integrated. However, as explained above, the MIC isolator of the prior art requires a magnet. There are caused problems when the conventional MIC isolator is enclosed in a airtight package together with semiconductor chips because of the size of magnet and gases arose from an adhesive used for securing the magnet to the substrate. Therefore, it was difficult to enclose the conventional MIC isolator in the airtight package together with semiconductor chips.
Thus, a package which contains the conventional MIC isolator and another package which does not contain the conventional MIC isolator must be separately provided in order to form one radio frequency circuit. Hence, it was difficult to make the radio frequency circuit compact and light.
FIG. 6 is a schematic diagram showing an equivalent circuit of a frequency converter using the conventional MIC isolator. In FIG. 6, RF signal 60 is supplied to MIC isolator 50. The output signal of MIC isolator 50 is supplied to MIC amplifier 64 composed of an MIC semiconductor. MIC amplifier 64 amplifies the signal supplied from MIC isolator 50. The output signal of MIC amplifier 64 is supplied to MIC mixer 66. MIC mixer 66 is also supplied with local oscillation signal 61. MIC mixer 66 converts the frequency of the signal supplied from MIC amplifier 64 using local oscillation signal 61. MIC mixer 66 outputs the resultant signal as IF signal 62.
MIC isolator 50 is enclosed in MIC isolator package 63 while MIC amplifier 64 and MIC mixer 66 are enclosed in MIC package 65.
Thus, in addition to the problem that the mounting area increases, there is caused another problem that impedance characteristics in high-frequency deteriorates because the signal must be transmitted between packages 63 and 65 via a long path.